Electronically energized heated seats are now increasingly available in motor vehicles. The seat warms a motor vehicle operator before the motor vehicle's heating system becomes effective. A typical automobile heating system can take five to ten minutes after the engine begins running before the thermostat opens. A heating element embedded within a seat starts to heat the motorist as soon as current flows through the heating element. A heated seat option may include resistive elements embedded within only the driver seat, or in some instances both the driver and passenger seat.
One control system primarily designed for use in controlling the actuation or energization of a heated seat is disclosed in U.S. Pat. No. 4,546,238 to Ahs. The control system disclosed in this patent utilizes the fact that the resistance of the resistive heating element changes with temperature. By monitoring a voltage signal generated across the resistance element, the temperature of the resistance element is determined. Comparator circuits in the control system energize and de-energize the resistive heating element to maintain the heating element temperature within a control range.
One potential problem that appears to have been overlooked in prior art heated seat systems is protection against electrical short circuits. A short in the control circuit of such a system can overheat the circuit and cause permanent damage. A large overcurrent might even cause the vehicle seat to catch on fire. Over current sensing and transient protection to prevent circuit damage due to high voltage spikes are necessary features in a reliable, safe heated seat system.